A typical cellular wireless network includes a number of base stations each radiating to define a respective coverage area in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In particular, each coverage area may operate on one or more carriers each defining a respective frequency bandwidth of coverage. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the network may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Further, a cellular wireless network may operate in accordance with a particular air interface protocol (radio access technology), with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) and Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between coverage areas, and other functions related to air interface communication.
In accordance with various industry standards, a base station may provide multiple cells in various directions and/or on various carrier frequencies, and each such cell may have a respective coverage identifier. For example, in accordance with a recent version of the LTE standard, each base station may have a global base station ID and each cell of a base station may have a cell ID. Thus, at the system level, each combination of global base station ID and cell ID may define a globally unique identifier for a cell. Generally, this globally unique identifier may be referred to as an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) cell global identifier (ECGI). Moreover, at the physical level, each cell provided by the base station also has a physical cell identifier (PCI) that is identifiable by a UE. While an ECGI is globally unique within a public land network, there are only 504 possible PCIs. Thus, PCIs are likely to be repeated many times throughout a public land mobile network.
In a system arranged as described above, each coverage identifier may be indicated to UEs by broadcast message(s) or the like of the respective cell. In this way, a UE could detect broadcast of coverage identifiers to facilitate attachment and/or handover processes.
For example, when a UE first powers on or enters into coverage of a wireless communication system, the UE may scan for pilot or reference signals and may determine a signal strength for each detected signal (e.g., a received strength or signal-to-noise ratio). Also, the UE may identify a cell providing the strongest pilot or reference signal, and may engage in a process to register with the network by transmitting an attach request to the base station that is providing that signal. The UE may then engage in attach signaling with the base station, by which the UE would register to be served by the base station on the identified cell. Through the attach process and/or subsequently, the base station and supporting network infrastructure may establish for the UE one or more bearers, essentially defining logical tunnels for carrying bearer data between the UE and a transport network such as the Internet. Once attached with the base station, the UE may then operate in a “connected” mode in which the base station may schedule data communication to and from the UE on the UE's established bearer(s).
In another example, a wireless communication system may support handover of a UE from one cell to another. For instance, when a first base station is serving a UE and the UE detects sufficiently strong coverage from a cell of a second base station, the UE may send a report to the first base station indicating the detected coverage identifier of the cell of the second base station. The first base station may in turn determine if applicable handover thresholds are met. If so, the first base station may engage in handover signaling via an interface with the second base station to orchestrate handover of the UE to the reported cell.